The present invention relates to electroluminescent (EL) lamps and more particularly to EL lamp structures that allow light to be emitted from the lamp structure in more than one direction. EL lamps are basically devices that convert electrical energy into light. AC current is passed between two electrodes insulated from each other and having a phosphorous material placed therebetween. Electrons in the phosphorous material are excited to a higher energy level by an electric field created between the two electrodes during the first quarter cycle of the AC voltage. During the second quarter cycle of the AC voltage, the applied field again approaches zero. This causes the electrons to return to their normal unexcited state. Excess energy is released in the form of light when these electrons return to their normal unexcited state. This process is repeated for the negative half of the AC cycle. Thus, light is emitted twice for each full cycle (Hz). Various properties of the emitted light can be controlled by varying this frequency, as well as the applied AC voltage. For example, the brightness of the EL lamp generally increases with voltage and frequency.
Prior art EL lamps typically comprise numerous component layers. At the light-emitting side of an EL lamp (typically the top) is a front electrode, which is typically made of a transparent, conductive indium tin oxide (ITO) layer and a silver bus bar to deliver maximum and uniform power to the ITO. Below the ITO/bus bar layers is a layer of phosphor, followed by a dielectric insulating layer and a rear electrode layer. All of these layers are typically disposed on a flexible or rigid substrate. In some prior art EL lamps, the ITO layer is sputtered on a polyester film, which acts as a flexible substrate. A relatively thick polyester film, typically four or more mils thick, is necessary because of the screen printing of the layers. The EL lamp construction may also include a top film laminate or coating to protect the component layers of the EL lamp construction.
Prior art EL lamps that emit light from the front and the back surfaces of the lamp are typically constructed simply by joining two separate unidirectional EL lamps back-to-back. Unfortunately, this type of construction has an increased overall thickness as compared to a single EL lamp. Furthermore, the power requirements for this type of back-to-back EL lamp are about twice that of a single EL lamp and the cost of manufacturing is almost double that of a single EL lamp.
The power constraint is a significant limitation :in small and lightweight electronic applications where small dry cells, such as button, coin or cylindrical cells, must be used. These constraints are even further limiting in applications where light emission in several directions is desired.
It is therefore an object of the present invention to provide a multidirectional EL lamp structure that provides light emission in two opposing directions without utilizing two separate EL lamp structures in a back-to-back configuration. it is also an object of the present invention to provide a multidirectional EL lamp structure that provides light emission in two opposing directions without a significant increase in the overall thickness of the EL lamp structure.
It is a further object of the present invention to provide an alternate EL lamp structure that provides multidirectional light emission from the surface of a three-dimensional object.
These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.
The present invention is an EL lamp structure that provides light emission from the front and back surfaces of the structure without utilizing two separate EL lamp structures in a back-to-back configuration. The EL lamp utilizes a transparent electrode layer, such as printable indium tin oxide (ITO), for both the front and the rear electrode layers of the EL lamp. Thus, emitted light is visible from both the front and the rear of the EL lamp through the transparent electrode layers.
In multidirectional EL lamp structure of the present invention, a phosphor layer is printed on the front side of a flexible dielectric film substrate. A front and rear transparent electrode layer, such as printable indium tin oxide (ITO), is printed on the phosphor layer and on the back surface of the dielectric film, respectively. An ITO sputtered polyester film can also be used so that the back surface of the dielectric film does not have to be printed with the ITO ink in order to create a rear transparent electrode layer. A front bus bar is then printed on the front transparent electrode layer. If the rear transparent electrode layer is printed ITO, a back bus bar is printed on the back transparent electrode layer. If sputtered ITO film is used for the back electrode, then a back bus bar may not be needed due to the typical higher conductivity of the sputtered ITO as compared to the printed ITO. The front and rear bus bars are typically printed with silver or carbon ink or combination of both. The application of a top and/or bottom laminate, lacquer, or the like is optional and helps protect the EL lamp structure from adverse environmental conditions, normal wear and tear, and electrical. hazards. A laminate or similar coating will particularly protect the phosphor layer from moisture damage.
In an alternate embodiment, a multidirectional EL lamp structure provides multidirectional light emission from the surface of a three-dimensional object. The three-dimensional object can take any form and is made of a conductive material, such as carbon, metal, plated plastic, or the like. The three-dimensional object acts as both a rear electrode and a substrate for the remaining layers of the EL lamp structure. A dielectric layer, such as barium titanate, is applied to the outside surface of the object. A phosphor layer is applied to the dielectric layer. A transparent electrode layer is then applied to the phosphor layer. After the transparent electrode layer is applied, a front bus bar and/or electrode contact is applied to the ITO portion of the three-dimensional object.